1. Technical Field
The present invention relates to an alignment method in which an alignment mark of a to-be-positioned member (hereinafter referred to as a positioned member) is aligned with a reference mark provided to an alignment mask, and to an alignment mask used in the alignment method. The invention particularly relates to an alignment method of a liquid-jet head unit in which a liquid-jet head as a positioned member is fixed to a fixing plate.
2. Related Art
An ink-jet recording apparatus such as an ink-jet printer or a plotter is provided with an ink-jet recording head unit (hereinafter referred to as a head unit) which includes an ink-jet recording head to eject ink in the form of ink droplets. The ink is stored in a liquid storing portion such as an ink cartridge or an ink tank. The ink-jet recording head has nozzle lines each of which is made of nozzle orifices which are arranged side by side, and the ink-droplet-ejection surface is protected with a cover head. The cover head includes a window frame portion which has: an orifice window portion provided on an ink-droplet-ejection surface side of the ink-jet recording head to expose the nozzle orifices; and a side wall portion formed by bending the window frame portion to a side surface of the ink-jet recording head. The cover head is fixed by joining the side wall portions to the side surfaces of the ink-jet recording head (for example, see JP-A-2002-160376 (Page 9, FIG. 3)).
Furthermore, when fixing members, such as a cover head and a fixing plate, are joined to a plurality of ink-jet recording heads, the positioning of the ink-jet recording heads to a predetermined position is performed by moving the ink-jet recording heads to the fixing members so that an alignment mark, which is provided to a nozzle plate and which has the same shape as that of a nozzle orifice, can match a reference mark provided to an alignment mask formed of a flat glass plate.
In an alignment method of such a head unit, a reference mark provided to a transparent member, such as a glass, used as a mask member, and an alignment mark provided to a nozzle plate are imaged at the same time using an imaging means including a microscope and a CCD camera, so that an image is captured, whereby alignment is performed while checking the image thus captured. However, since the alignment mark is formed of a penetrated hole having the same shape as that of a nozzle orifice as described above, the alignment mark is imaged in a black color in the image captured by the imaging means. At this time, since the alignment mark is black, the reference mark is imaged in white to increase the contrast ratio to the alignment mark. Furthermore, the background of the image captured by the imaging means is shown in a whitish color close to a white color due to light reflected on the surface of the nozzle plate.
Here, suppose a case where image processing is performed on the captured image to detect the boundaries between the alignment mark and the background and between the reference mark and the background. In this case, since the contrast ratio between the whitish background being close to a white color and the blackish alignment mark is high, the boundary of the blackish alignment mark can be detected with high accuracy. However, since the transparent member such a glass is used for the alignment mask, the background color of the nozzle plate is imaged through the alignment mask using the imaging means, so that the contrast ratio is low between the background close to a color white, and the whitish reference mark. Accordingly, unevenness occurs on the boundary of the reference mark. Consequently, the boundary of the reference mark cannot be detected with high accuracy, and a decrease in alignment accuracy comes up as a problem.
Note that, such a problem exists not only in the alignment method of a liquid-jet head unit such as an ink-jet recording head unit, but also in an alignment method in which an alignment mark of a positioned member is aligned with a reference mark provided to an alignment mask.